The present invention relates generally to a keyboard for entering information in an electronic device and, in particular, to a keyboard with status keys such as the ALT, CTRL, SHIFT keys in addition to the alphanumeric keys.
It is known that when a plurality of on-off switches SW1, SW2 and SW3 are connected to a series of resistors R1, R2, R3 and R4, as shown in FIG. 1a, it is possible to identify which one of the switches is closed by measuring the resistance r1 between point A and point B and the resistance r2 between point B and point C, and calculating the ratio r2/r1, For example, if SW3 is closed while SW2 and SW1 are open, the ratio is given by r2/r1=R4/(R1+R2+R3). Similarly, if SW2 is closed while SW1 and SW3 are open, the ratio is given by r2/r1=(R3+R4)/(R1+R2). In particular, if point C is connected to circuit ground G and point A is connected to a power source having a known voltage V relative to the ground G, as shown in FIG. 1b, it is sufficient to measure the voltage V1 at point B in reference to V, or the voltage V2 at point B in reference to the ground G. As shown in FIGS. 1a and 1b, the switches SW1, SW2 and SW3 are connected to the series of resistors R1-R4 at different locations J1, J2 and J3. Thus, it is possible to find out the location at which the switch is closed from the measured voltage V1 or V2. Alternatively, it is possible to measure the current I drawn through the resistors R1, R2, . . . by measuring the electrical potential or voltage between point V and point Vr, which is the voltage across a reference resistor Rr, as shown in FIG. 1c. From the known current I, it is sufficient to measure either V1 or V2 to identify the closed switch and the associated location.
The potentiometer-like arrangement, as shown in FIGS. 1a-1c, can be used to construct a keyboard for entering information in an electronic device. For example, the switches SW1, SW2, . . . can be used as the number keys representing numerals 1, 2, . . . in a telephone keyboard for dialing.
In a circuit board, it is possible to build a keyboard using discrete resistors by electrically connecting the connectors of each discrete resistor to a printed circuit, for example. It is also possible to print a thick-film material directly onto the circuit board to form the series of resistors. It is further possible to use a single resistive strip R, as shown in FIG. 2a, to replace the series of discrete resistors R1, R2, . . . , in a keyboard arrangement, or two resistive strips R and Rxe2x80x2, as shown in FIG. 2b, to replace the series of discrete resistors. Resistive keyboards, as shown in FIGS. 2a and 2b, are compact, rugged and cost-effective. The number of I/O pins in a resistive keyboard, in general, is much smaller than that in a regular keyboard. A reduced number of I/O pins is especially beneficial in a hand-held electronic device such as a Nokia Communicator, which has 64 keys.
It is advantageous and desirable to improve the resistive keyboard to include status keys such as the ALT, SHIFT and CTRL keys for changing the meaning or function of other keys as in a QWERTY keyboard, while keeping the number of I/O pins small.
It is the primary objective of the present invention to provide a keyboard with status keys for changing the meaning or function of other keys in the keyboard by pressing one or more status keys when at least one of the other keys is pressed, wherein the status keys are separately connected to a series of resistors, each having a different resistance to identify the pressed status key.
According to the first aspect of the present invention, a keyboard for entering information in an electronic device comprising a plurality of first keys electronically connected to a series of first resistors at a plurality of locations for providing a first signal when one of the first keys is pressed, wherein the first signal is indicative of the location of the pressed first key; a plurality of second resistors connected in series to the series of first resistors, wherein each second resistor has a different resistance; and a plurality of the second keys separately connected in parallel to the second resistors for selectively by-passing the second resistors when one or more second keys are pressed, wherein a second signal is provided when one of the first keys is pressed together with at least one second key, and wherein the second signal is indicative the resistance of the at least one pressed second key.
Preferably, the first resistors are provided in a form of one or more resistive strips.
Preferably, the first keys include alphanumeric keys, each representing a different alphanumeric value and the second keys include status keys for changing the alphanumeric value.
According to the second aspect of the present invention, a method of arranging a keyboard for entering information in an electronic device comprising the steps of providing a plurality of first resistors connected in series; providing a plurality of first keys electronically connected to the series of first resistors at a plurality of locations for providing a first signal when one of the first keys is pressed, wherein the first signal is indicative of the location of the pressed first key; providing a plurality of second resistors connected in series to the series of first resistors, wherein each second resistor has a different resistance; and providing a plurality of second keys separately connected in parallel to the second resistors for selectively by-passing the second resistors when one or more of the second keys are pressed, wherein a second signal is provided when one of the first keys is pressed together with at least one second key, and wherein the second signal is indicative of the location of the pressed first key and the resistance associated with the at least one pressed second key.
According to the third aspect of the present invention, an electronic device comprising a keyboard for entering information, wherein the keyboard comprises a plurality of first keys electronically connected to a series of first resistors at a plurality of locations for providing a first signal when one of the first keys is pressed, wherein the first signal is indicative of the location of the pressed first key; a plurality of second resistors connected in series to the series of first resistors, wherein each second resistor has a different resistance; and a plurality of second keys separately connected in parallel to the second resistors for selectively by-passing the second resistors when one or more second keys are pressed, wherein a second signal is provided when one of the first key is pressed together with at least one second key, and wherein the second signal is indicative of the resistance of the at least one pressed second key. The keyboard further comprises means, responsive to the first and second signal, for identifying the pressed first and second keys, and means for processing information based on the identified first and second keys.
The present invention will become apparent upon reading the description taken in conjunction with FIGS. 3 to 6c.